Parasitic effects from measurement fixtures are difficult to handle in microwave characterization of small devices and materials. It is even more challenging when the expected signal level is low. Such devices include magnetroelectronic/spintronic devices and high-impedance devices, for instance a metallic single-walled-carbon-nanotube (mSWNT), a SWNT transistor, a minimum-size deep-submicron metal-oxide-semiconductor (MOS) field-effect-transistor (FET), a sub-micron MOS FET that is operating in sub-threshold region, and a molecular device. Such materials include on-chip biofluids, chemicals and thin films. The microwave characteristics of these devices and materials are of great interest in their development and applications. Considering a metallic SWNT as an example; its high-frequency characteristics are important for potential interconnect and sensor applications. Metallic SWNTs are also considered an ideal, one-dimensional model for fundament condensed matter physics studies. Their high-frequency properties, which correspond to collective Plasmon oscillations, would be a direct verification of Luttinger liquid theory that was proposed to describe one-dimensional material.
A proposed RF transmission line model as illustrated enclosed in the dashed-line box 130 in FIG. 1(c), has often been the focus and foundation for previous mSWNT studies. It has been predicted that mSWNTs have very high characteristic impedance, on the order of 10 kΩ due to high kinetic inductance and includes a large contact resistance component of a few kΩ or higher. Under these conditions, signal attenuation and reflection are very high when currently available microwave measurement systems are used for their characterizations. The difficulty is further complicated by the parasitic effects coming from RF test fixtures, especially the effects from gap coupling capacitor equivalently illustrated at C′p (FIG. 1(c)) and Cp (FIG. 1(d)), in typical measurement arrangements.
The calculated scattering parameters, S21, of the equivalent circuit 140 (FIG. 1(d)) as illustrated in FIGS. 2(a) and 2(b) of several situations exemplify the measurement challenge. At low frequencies, the contact resistance (R) dominates; at high frequencies, the coupling capacitance (Cp) dominates. The inductance effect, which is an indication of transmission line characteristics is indistinguishable from the combined coupling capacitance and contact resistance effects. Moreover, measurement uncertainties, including contact uncertainties from one measurement to another, make it difficult to use various de-embedding or off-chip approaches that have been developed for deep sub-micron CMOS device characterizations. As a result, only limited success has been achieved in the efforts on high-frequency mCNT property and potential application investigations. These efforts include the development of measurement methods for CNT devices. Previously attempted direct scattering parameter measurements, resonant circuit techniques, and heterodyne methods have not been successful in addressing the measurement difficulties for the characterization of the equivalent transmission line model of a mCNT. For instance, the exceptionally large and unique “kinetic” inductance associated with mCNTs has not yet been experimentally verified and characterized.
While various measurement methods for characterizing CNT devices have been developed, no design has emerged that generally encompasses all of the desired characteristics as hereafter presented in accordance with the subject technology.